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Fingerprints reveal clues to suspects’ habits

By Tom Simonite

Fingerprints from a crime scene are useless if the perpetrator’s prints are not on file. But new forensic techniques now mean they can be used to determine whether a person is a smoker, uses drugs, and even which aftershave they wear – information that could help narrow down suspects.

Fingerprints contain a mixture of skin cells, sweat secretions and substances picked up from elsewhere. Careful analysis can show whether a person may have handled drugs or explosives, but the new tools make it possible to determine a person’s habits from the secretions in their prints as well.

“We have found you can detect cotinine, made when someone metabolises nicotine, in fingerprints,” says Sue Jickells, an analytical chemist at Kings College London, UK. “This tells you if that person is a smoker, and this kind of additional information could be useful if you don’t have a suspect.”

Jickells plans to collect prints from addicts at heroin and crack cocaine clinics to see if these drugs can be detected in fingerprints residue too. And she has shown that traces of cosmetics can be found left behind in prints. “In one sample we picked up some hair product that was eventually linked back to one of our students,” she says.

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Fat fingerprint

For about five hours after application, aftershave is also left behind, she says. “It is currently difficult to differentiate different kinds of product,” Jickells adds. “But I think in the future biosensors will be used to easily tell them apart.”

Jickells is also looking at differences in individual fingerprint chemistry. Much of the material of a fingerprint consists of lipids – fat secreted by pores in the skin.

“It seems people differ in the amount they secrete of the different kinds of lipid,” Jickells says. “The differences aren’t great enough to be able to identify someone specifically, but you could definitely rule out suspects if you found they had produced a lot of one lipid, in contrast to a print at the crime scene.”

Nanoparticle tags

A particularly quick method of analysing fingerprints has been developed by David Russell, a chemist at the University of East Anglia, UK, who has also developed a way to tell if a fingerprint was left by a smoker.

Russell coated gold nanoparticles with an antibody specific to cotinine, and labelled the particles with a fluorescent protein. A solution containing the particles is then applied to a fingerprint and illuminated with light.

The fluorescent particles then show up under the light if the print is from a smoker. “The idea is to develop something for first responders, so they can quickly find out more about a suspect,” Russell says.

Russell’s nanoparticle method has also been used to develop a quick check for toxins like ricin and cholera. Particles are coated with a sugar that binds to the toxins and dissolved in a coloured solution. If a sample containing the toxin is added to the solution, the particles immediately clump together and scatter light differently. This causes the solution to quickly change colour. “It’s a simple, quick, yes-or-no detection method,” Russell says.

Russell’s team hopes to adapt the technique to speed up detection of the H5N1 strain of avian influenza, or bird flu. Currently, samples must be sent away for lab analysis, so a portable detector could see potential outbreaks confirmed rapidly in the field.